Excessive energy consumption is widely regarded as the biggest problem with drones and other small flying vehicles. Batteries can only store so much power, which significantly limits the flight time of aerial vehicles. Increasing battery capacity is no solution either—that increases the weight of the aerial vehicle, which again limits flight time. If drones are ever going to fully deliver on their potential with real-world performance, further technological innovation will be required.
For the smallest of flying robots, a group of researchers at Princeton University and the University of Illinois Urbana-Champaign believe they have a better path forward. Inspired by the incredible ability of grasshoppers to glide for long distances, they have developed a model that could help tiny aerial vehicles to fly long distances using minimal amounts of energy.
3D-printed wings that mimic those of grasshoppers (📷: Sameer A. Khan)
Grasshoppers may not be the first creatures that come to mind when thinking about efficient flight, but these insects have a valuable trick that most robotic flyers lack. In addition to flapping their wings to generate thrust, grasshoppers can fully deploy their hindwings and glide, allowing them to travel significant distances while expending very little energy. According to the researchers, this ability to alternate between powered flight and gliding is what makes grasshoppers such a promising model for insect-scale robots.
The team focused their study on the hindwings of the American grasshopper, Schistocerca americana. Unlike the leathery forewings, which primarily serve a protective role, the hindwings are large, membranous, and capable of both flapping and gliding. Notably, these wings are corrugated, with a series of ridges and valleys that allow them to fold neatly when not in use.
To understand which features of the wing were most important for efficient gliding, the researchers conducted detailed CT scans of real grasshopper wings. Using this data, they created 3D-printed wing models that isolated specific characteristics, such as planform shape, camber profile, and corrugation patterns. These models were tested in water channel experiments to measure aerodynamic performance before being incorporated into small, grasshopper-inspired gliders.
Members of the research team (📷: Sameer A. Khan)
It was found that while corrugated wings produced high aerodynamic efficiency at low angles of attack, their performance dropped off at steeper angles. In contrast, wings that captured the overall planform shape of the grasshopper hindwing while using a simplified, smooth camber profile delivered consistent efficiency across a wide range of flight conditions. When launched across the Princeton Robotics Laboratory, these smooth-winged gliders demonstrated repeatable and reliable flight performance comparable to that of real grasshoppers.
The findings suggest that wing shape and camber are more critical to efficient gliding than corrugation alone. The corrugations, the team believes, may primarily serve to enable wing folding and deployment rather than to maximize aerodynamic efficiency.
By incorporating gliding into the flight repertoire of insect-scale robots, engineers could dramatically reduce power consumption, enabling untethered flight with smaller batteries. This, in turn, opens the door to the development of future robots capable of multimodal locomotion—crawling, jumping, flapping, and gliding as needed.